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QTc Formula (Bazett):
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The QTc (Corrected QT Interval) calculation adjusts the QT interval for heart rate using Bazett's formula. This provides a standardized measure of ventricular repolarization that accounts for variations in heart rate.
The calculator uses Bazett's formula:
Where:
Explanation: The formula corrects the measured QT interval for heart rate by dividing by the square root of the RR interval, providing a heart rate-independent measure of ventricular repolarization.
Details: QTc calculation is essential for assessing cardiac repolarization abnormalities, identifying patients at risk for arrhythmias, and monitoring drug effects that may prolong QT interval.
Tips: Enter QT interval in milliseconds and RR interval in seconds. Both values must be positive numbers. The RR interval should be measured from the ECG as the time between consecutive R waves.
Q1: What is a normal QTc value?
A: Normal QTc values are typically <440 ms for men and <460 ms for women. Values above these thresholds may indicate prolonged QT syndrome.
Q2: Why use Bazett's formula?
A: Bazett's formula is the most widely used and clinically accepted method for QT correction, though it may overcorrect at very high heart rates.
Q3: When should QTc be measured?
A: QTc should be measured in patients taking medications known to prolong QT interval, those with syncope or family history of sudden cardiac death, and in routine ECG interpretation.
Q4: Are there limitations to Bazett's formula?
A: The formula may be less accurate at extreme heart rates (<60 or >100 bpm) and alternative formulas (Fridericia, Framingham) may be used in these cases.
Q5: How is RR interval measured?
A: RR interval is measured from the beginning of one QRS complex to the beginning of the next QRS complex on an ECG, typically converted to seconds for calculation.